The invention relates to a device for controlling light sources having a ballast.
Such devices are a component of ballasts for electric light sources and are intended for use in lighting systems whose light sources are switched on and off and dimmed with the aid of a central operator""s or control console. Usually, a plurality of light sources, for example the light sources of a room, are jointly controlled by a control element of the control console. These light sources, which are combined into a group, are switched on and/or off or dimmed by actuating the same control element. By actuating a control element, for example a dimmer, a brightness set point is prescribed for a group of light sources, and converted with the aid of a device into a corresponding control signal which is used for brightness control of the light sources connected to the ballasts. The value of the control signal required for this depends, on the one hand, on the prescribed brightness set point and, on the other hand, on the type of the light sources to be operated.
European Laid-Open Specification EP 0 688 153 A2 discloses a circuit arrangement for controlling the brightness and the operational performance of gas discharge lamps. The circuit arrangement has a receiving device which can be fed commands for controlling the brightness of gas discharge lamps via a digital control input. These commands are converted into a corresponding control voltage for setting the desired brightness of the gas discharge lamps by means of a function element which acts in a logarithmic or exponential fashion. The function element acting in a logarithmic or exponential fashion is specifically tuned to the brightness control of gas discharge lamps and permits only inadequate brightness control with other types of light sources, since a transfer function for adapting the light source to the physiological sensitivity of the human eye is required.
It is the object of the invention to provide a device for controlling light sources having a ballast, which renders it possible in the case of lighting systems with light sources of different type to reduce and/or to increase the brightness of these light sources jointly and to the same extent.
According to the invention, this object is achieved for a device of, the generic type by the characterizing features of Patent Claim 1. Particularly advantageous designs of the invention are described in the subclaims.
The device according to the invention for controlling light sources having a ballast can be connected to a set point generator for setting a brightness set point for the light sources, and has means for generating a control signal, dependent on the set point of the set point generator, for brightness control of the light sources, as well as means for adapting the control signal to different types of light sources. This ensures that different types of light sources which are combined in a lighting system into a group of light sources to be jointly switched can be dimmed to the same extent. It is ensured, in particular, that, owing to the prescription of a brightness set point for the aforementioned group of light sources, each of these light sources is operated with the same dimming level even when they are of different type. The same dimming level means here that the light sources in this operating state output the same relative luminous flux in each case. For example, the prescription of the dimming level at 70% means that each light source of the group outputs 70% of its maximum luminous flux. The device according to the invention converts the brightness set point prescribed by the set point generator into a control signal which is adapted to the type of light source to be operated and is used for brightness control of the light sources.
The means for generating the control signal or/and the means for adapting the control signal to different types of light sources advantageously include means for generating first control signal values whose dependence on the set point can be described by a first control signal set point characteristic curve, and means for generating second control signal values and possibly further control signal values whose dependence on the set point can be described by a second control signal set point characteristic curve and/or by further control signal set point characteristic curves, and, furthermore, means for selecting the first control signal values or the second control signal values or the possibly further control signal values such that the first or the second or the possibly further control signal values can optionally be used for brightness control of the light sources. As a result, the device according to the invention can be used to adapt the control voltage to at least two different types of light sources, which require a different control signal for setting the desired brightness set point. The first control signal set point characteristic curve advantageously has a substantially linear course, and the second control signal set point characteristic curve advantageously has a nonlinear, preferably a substantially exponential or logarithmic course, or one which can be represented by a polynomial of higher degree. The control signal set point characteristic curve with the substantially linear course is tuned to the brightness control of incandescent lamps, and the control signal set point characteristic curve with the non-linear course is tuned to the brightness control of fluorescent lamps.
The means for adapting the control signal to different types of light sources advantageously comprise a programmable microprocessor or a programmable logic circuit or an analogue circuit which can be operated in a program-controlled fashion. In these cases, the aforenamed different control signal set point characteristic curves can be stored in a fashion capable of being called in a nonvolatile storage means. The means for selecting the first or second and/or further control signal values are advantageously designed as switching means which render it possible to switch over between the corresponding control signal set point characteristic curves. It is possible in this way to adapt the control signal to the type of the light sources to be operated by switching over manually or automatically to the corresponding control signal set point characteristic curve. However, it is also possible to design the means for selecting the first or the second and/or the further control signal values as control signal outputs such that at least one separate control signal output is respectively assigned to the first and the second as well as the possibly further control signal values.
The device according to the invention is advantageously accommodated in a separate housing and has at least one control signal output to which at least one ballast can be connected. The device according to the invention can, however, also be designed as a component of a ballast for electric light sources.